The objective of this proposal is to improve our understanding of the molecular mechanism of genetic recombination and related cellular functions such as the induction of SOS functions. The proposal described here consists of three major research projects which we have been working on for the past several years. One is related to the genetic transformation in E. coli K12 with special emphasis on the establishment of high frequency transformation, transfection and plasmid transfer system, and studies on the molecular mechanism of transformation mediated recombination. The second project is concerned with the structure and function of one of the rec enzymes, recBC-DNase. We will study the subunit structure of the DNase and the reconstitution process in order to understand the molecular mechanism of the complicated enzyme reactions associated with the enzyme. We will attempts to isolate a (Hypothetical) protein component which plays a role in protecting linear phage DNA against recBC-DNase upon infection. The third project deals with the molecular mechanism of induction of SOS functions. Using our biochemical read-through assay procedure, the permeable cell induction system and other genetic as well as biochemical means, we will try to understand the molecular basis of the early events which lead to the induction of SOS functions. The isolation and identification of the signal substance is the primary aim of this part of my research proposal.